One conventional integrated network switch is represented by the 20-20.RTM. integrated network switch manufactured by Harris Corporation. This integrated network switch, the subject of U.S. Pat. No. 4,688,212 which issued on Aug. 18, 1987 to MacGinitie et al. and assigned to Harris Corporation, accommodates both the North American (.mu.-Law) and the European (A-Law) multiplex equipment, while processing both synchronous and asynchronous circuit- and packet- switched data up to 2 Mbits/s.
A complete understanding of the invention described hereinafter will be facilitated with a description of the construction and operation of the 20-20 switch. The hardware of this microprocessor based system includes peripheral cards bearing telephony interface units which contain circuits for lines, trunk, and service units. Service units may be DTMF receivers, MF receivers, serial interface units and the like. A common controller interconnects to the peripheral cards through a telephony bus. The common controller consists of a telephony control unit (TCU) and a call processor unit (CPU).
The integrated network switch can provide up to 2048 ports and accommodate up to 1920 non-blocking peripheral devices, such as telephones, printers, modems, tape drives, data devices and the like, grouped into port groups as will be described. Each port group contains up to 32 peripheral interface units and is associated with a port group bus, the port group buses forming a portion of the telephony bus to be described. Thus, 60 port group buses are provided to accommodate 1920 peripheral devices (32.times.60=1920). The remaining 128 ports, corresponding to 4 additional port groups, are allocated to tone and conference functions.
The peripheral circuits are coupled to a telephony control unit (TCU) through the telephony bus, which as will be explained in more detail herein below is actually a large set of small buses that form a part of a multiplexing tree. The telephony bus connects all line, trunk, other telephony and data feature units to the telephony controller and also provides timing for codecs and similar devices. The telephony control unit mediates all communications between the peripherals and the call processor unit (CPU) of the common controller. Thus, the call processor unit and the telephony control unit together constitute a common control for the peripherals. Therefore. the integrated network switch can be viewed generally as consisting of (1) telephony peripherals, (2) a telephony bus tree, and (3) a common controller containing a telephony controller unit (TCU) and a call processor unit (CPU). The peripherals communicate with the TCU through the telephony bus tree, and subsequently with the CPU through the TCU.
The telephone control unit (TCU) not only mediates all communications between the call processor unit and the peripherals, it also scans the peripherals for service requests, provides the switched voice/data connections to devices, and provides timing for the PCM, codecs, and data. The TCU appears to the call processor unit (CPU) as 32 Kbytes of memory divided into 2048 blocks of 16 bytes each. One block is designated for each address. All functions associated with a given peripheral appear in the 16 byte block assigned to the peripheral.
The call processor unit (CPU) is a bus-oriented microprocessor complex. Typically the CPU consists of a service unit, multiple microprocessors, dual port DRAMs, and a disk subsystem. More specifically, a dual port DRAM is associated with each microprocessor and operates to store code loaded from disk and supply instructions to the associated processor. Further, the service unit provides clocks and priority resolver for the bus, cross-coupled state register and interrupts for active/standby and switch-over control, the interface to the telephony controller unit, and the signaling packet transfer (SPT) function for data communication with the peripherals.
As explained previously, the telephony bus tree consists of a set of buses forming a multiplexing tree between the peripheral devices and the common control. In the exemplary integrated switch network, with 1920 peripheral devices, there are 60 buses each assigned to a port group of 32 ports. Since each bus operates at the standard 2.048 Mhz rate, 32 bytes of PCM data will be transmitted in a 125 .mu.s frame divided into 32 time slots. It should be apparent that with the arrangement described each of the 1920 peripheral devices transmits a byte of PCM data during each frame interval. That is, all peripherals will be able to transmit in each frame.
Signaling information, that is digital data not constituting PCM voice information, is transmitted utilizing a 16 frame submultiplexing cycle or superframe. As is known in the art, signaling information and PCM voice information are transmitted over separate wires between a peripheral and the common control. That is, the bus to a peripheral is not a single wire, but a plurality of wires each connected to carry a different type of information. For example, a suitable bus may consist of 7 wires. Two wires are assigned to PCM data, one for PCM transmission the other for PCM reception. Two additional wires are assigned to carry signaling information, one for signaling information transmission, the other for signaling information reception. A sixth line is provided to carry clock signals, while the seventh line is the ground line. Thus, all bits of all time slots are available for PCM and data.
The above described integrated network switch works well and provides a cost effective, easily expandable switch. However, it has constraints which limit its applicabilities. For one, the design limits the distance peripheral cards are from the common control circuitry. Further, the number of ports is limited to 2048 ports.